Um, no. Well, sorta, in that it can use LLVMpipe to JIT the software rendering. Generally, on Linux, the hardware does the hardware acceleration (using the proprietary blobs or the free driver equivalents). Like on Windows, you link against the GL API provided by Mesa but the runtime is provided by the hardware vendors (through kernel DRM -- direct rendering module). That's one reason why installing the nVidia drivers from nVidia is bad: they blow away the Mesa libraries, which means if you're a developer and upgrade the -dev package you will experience open running sores and purulent boils.

Um, no. Well, sorta, in that it can use LLVMpipe to JIT the software rendering. Generally, on Linux, the hardware does the hardware acceleration (using the proprietary blobs or the free driver equivalents).

Um, yes. Well, sorta. Most of the open source hardware 3D drivers use Mesa as a front end - a bit like Microsoft writing D3D and the hardware manufacturers only needing to write a relatively small hardware specific bit rather than a full 3Dstack like they do with OpenGL.